1. Field of the Invention
The present invention relates to an inverter control apparatus.
2. Background of the Invention
Generally, an inverter is a power conversion device that receives commercial alternating current (AC) power, converts the AC power into direct current (DC) power, re-converts the DC power into AC power suitable for a motor, and supplies the AC power to the motor. Such an inverter efficiently controls a motor to decrease power consumption of the motor, thereby improving energy efficiency.
In many application loads of industrial fields, an inverter is controlled by a voltage/frequency (abbreviated as “V/F” hereinafter) control method, the control method is mainly used in fields such as a fan, a pump, and a blower that do not require fast dynamic characteristics in a driving area below a rated speed.
Also, in an ascending/descending load such as an elevator or a crane, an encoder, which is a position sensor for measuring an absolute position of a motor or a relative position of the motor according to a rotation state of the motor, may be used to precisely control a speed and thus achieve high starting torque performance. However, in some systems, V/F control is performed due to costs incurred for maintenance of an encoder.
However, when an inverter is controlled by V/F control, starting torque may be insufficient due to a voltage drop caused by stator resistance and leakage inductance of a motor in a slow driving area in which an output voltage of the inverter is low. Also, a starting failure due to the insufficiency of the starting torque causes an excessive current, which may cause a failure of the inverter or a failure of the motor.